Method for reception by a terminal of contents broadcast by a plurality of channels through a computer network

ABSTRACT

A method of reception by a terminal (T) of contents broadcast over a computer network via two or more broadcast channels (CD 0 , CD 1 ), and a terminal for implementing the method. A signaling channel (CS 0 ) is associated with the first broadcast channel (CD 0 ) and the terminal (T) acquires said signaling channel (CS 0 ) and switches from the first broadcast channel (CD 0 ) to the second broadcast channel (CD 1 ) via said signaling channel (CS 0 ).

The present invention relates to a method of reception by a terminal ofcontent broadcast by a plurality of channels via a computer network.

Many television stations broadcast their programs from a broadcastsource via a hierarchy of local relay transmitters covering a givengeographical area. Each relay transmitter receives an audiovisual signalconveying the program being broadcast and transmits it to other relaytransmitters in order to route it from the source to the receivers. Arelay transmitter can temporarily interrupt the received program andtransmit a different program instead. This is referred to as “handover”and is used by some national stations, which generally have only onebroadcast channel, to broadcast regional programs between two nationalprograms. During “handover” periods, receivers in a given region canreceive only the program for that region, to the exclusion of otherregional programs.

Some television stations also broadcast programs, more usually referredto in this case as “content”, over the Internet, generally using a“multicast” broadcasting method which consists in a source S sending IPdata packets conveying the content to be broadcast via the Internet in asingle sending. The IP packets are then duplicated by “routers”, i.e.nodes of the network, and routed via the Internet to the receiverterminals. To receive a content, each receiver terminal must firstrecover a session description protocol (SDP) file associated with thesource S, for example by downloading it from a website. The structure ofan SDP file is defined by the Internet Engineering Task Force (IETF) inthe document RFC 2327. The file conveys information required forreceiver terminals to receive multimedia content broadcast by the sourceS. For each source S there is a general SDP file containing all theinformation required to receive from the source S, regardless of thecontent it is broadcasting. For each broadcast content (TV transmission,film, conference, etc.) there is also a specific SDP file containing allthe information needed to receive that particular content. The generalSDP file of the source S is valid regardless of the content that thesource is broadcasting, whereas the SDP file of a specific content isvalid only for the broadcasting of that content. If a terminal wishes toreceive a multimedia content broadcast by the source S, it sends arequest to acquire that content to the source S via the Internet usingthe Internet Group Management Protocol (IGMP). The first router thatreceives the request and is already receiving the IP packets broadcastby the source S duplicates the IP packets and then routes them to theterminal or to another router nearer the terminal. Because the contentis sent by the source S in one sending, the multicast technique is notgreedy in terms of bandwidth. The same station could therefore broadcastdifferent contents simultaneously over different broadcast channelswithout unacceptably increasing its bandwidth consumption. However, toreceive the various channels, the receiver terminals would have torecover as many SDP files as there are channels that can be received andestablish the link between the channels for themselves.

The technical problem addressed by the present invention is thereforethat of proposing a method of reception by a terminal of two or morebroadcast channels that provides a simple way for the terminal to changechannel.

To this end, the invention consists in a method of reception, by aterminal, of content broadcast over a computer network by a plurality ofbroadcast channels forming a group of channels linked in accordance witha given organization, in which method:

-   -   each broadcast channel is associated with a signaling channel        conveying information for acquiring said broadcast channel,    -   the terminal acquires a first signaling channel associated with        a first broadcast channel and, from said first signaling        channel, starts to receive the first broadcast channel, and    -   to switch from the first broadcast channel to a second broadcast        channel linked to the first broadcast channel, the terminal        acquires a second signaling channel associated with a second        broadcast channel from the first signaling channel and, from the        second signaling channel, starts to receive the second broadcast        channel.

The signaling channel associated with the broadcast channel carries allthe information needed for the terminal to acquire the broadcastchannel. Accordingly, to switch to a given broadcast channel, theterminal first acquires the associated signaling channel. In the priorart, the broadcast channels were independent of each other and usedexclusively to carry broadcast content. The invention therefore consistsin linking the broadcast channels by way of a signaling channel toenable the terminal to switch from one broadcast channel to another.

To switch from the second broadcast channel to the first broadcastchannel, the terminal advantageously acquires the signaling channelassociated with the first broadcast channel from the signaling channelassociated with the second broadcast channel. Accordingly, afterswitching from the first broadcast channel to the second broadcastchannel, the terminal can return to the first broadcast channel via thesignaling channel associated with the second broadcast channel.

The signal channel associated with one of the broadcast channelspreferably indicates to the terminal whether the two broadcast channelsare broadcasting simultaneously or alternately. When the terminal isreceiving a given broadcast channel, thanks to the associated signalingchannel, it can tell whether it can change channel during thebroadcasting of content via the current channel or must wait for the endof the current broadcast.

The signaling channel associated with one of the broadcast channelsadvantageously supplies the terminal with a computer address of thesignaling channel associated with the other broadcast channel. Theterminal can use this address to cover the corresponding signalingchannel.

The signaling channel associated with one of the broadcast channels cansupply the terminal with an indication of the starting of broadcastingvia the other broadcast channel and/or an indication of the stopping ofbroadcasting via the other broadcast channel. Accordingly, when theterminal is receiving one of the two broadcast channels, it does notneed to change broadcast channel to find out if the other channel isbroadcasting a content. That information is supplied to it directly bythe signaling channel associated with the broadcast channel it isreceiving. Furthermore, using the end-of-broadcast indication, theterminal can automatically change broadcast channel at the end of abroadcast without intervention by its user.

During reception of the content broadcast by one of the broadcastchannels, the terminal advantageously informs a user of parallelbroadcasting over the other broadcast channel, and changes broadcastchannel in response to a switching command from said user. For example,while the terminal is receiving one broadcast channel, it can display anicon indicating that a broadcast is taking place on the other broadcastchannel. To change broadcast channel it suffices to select the icon.

With contents being broadcast over a plurality of broadcast channelsrespectively associated with a plurality of signaling channels andforming a group of channels, each signaling channel advantageouslysupplies the terminal with the information for acquiring one or moreother signaling channels associated with another broadcast channel ofthe same group so that the terminal can access all the broadcastchannels of the group.

In one particular embodiment, the group of channels comprises a mainchannel and a plurality of secondary channels, and the signaling channelassociated with the main channel supplies the terminal with theinformation to acquire signaling channels associated with all thesecondary channels.

The signaling channel associated with each secondary channeladvantageously supplies the terminal with information for acquiring thesignaling channel associated with the main channel, to the exclusion ofinformation for the signaling channels associated with the othersecondary channels.

In this embodiment of the invention, the terminal can switch from themain channel to any secondary channel. However, it must switch from onesecondary channel to another secondary channel via the main channel.This prevents overloading the signaling channels associated with thesecondary channels with information, and consequently limits theconsumption of bandwidth, and facilitates updating the signalingchannels.

The invention also consists in a terminal for implementing the methoddefined above, comprising means for acquiring a signaling channelassociated with a broadcast channel and means for switching from saidbroadcast channel to another broadcast channel with the aid of saidsignaling channel.

The invention will be better understood in the light of the followingdescription of an implementation of a reception method and a terminal inaccordance with the invention, which description is given with referenceto the accompanying drawings, in which:

FIG. 1 is a diagram showing a source, with broadcast and signalingchannels, a website, the Internet, a receiver terminal, and varioussteps of this implementation of a method of the invention;

FIG. 2 is a flowchart of the main steps of the FIG. 1 method; and

FIGS. 3 to 7 are flowcharts of substeps of the FIG. 2 method.

FIG. 1 shows a broadcast source S, a receiver terminal T, a website SWand the Internet.

In the particular example described here, the source S is a nationaltelevision station called “TV1” hosted by an audiovisual Internet serverand adapted to broadcast content in the form of audiovisual programs(television broadcasts, video films, etc.) to receiver terminals via theInternet in multicast mode, nationally and regionally. The audiovisualserver could host other broadcast sources. The multicast mode ofbroadcasting consists in sending IP data packets carrying the content tobe broadcast from the source S in one sending. The IP data packets arethen duplicated by a cascade of Internet routers and routed to thereceiver terminals via the Internet. The source S has a main channel CD0for broadcasting national programs and a plurality of secondary channelsCD1, CD2, . . . , CDi, . . . , CDn for broadcasting regional programs. Asignaling channel CSi is associated with each broadcast channel CDi andis adapted to carry information needed for a terminal to start receivingthe broadcast channel CDi.

A programming center, not shown, draws up a schedule of programsbroadcast from the source S and creates SDP files relating to thesignaling channels CSi associated with the broadcast channels CDi of thesource S.

The IETF defines the structure of an SDP file as follows:

-   -   v=(protocol version)    -   o=(owner/creator and session identifier)    -   s=(session name)    -   i=* (session information)    -   u=*(URI of description)    -   e=*(email address)    -   p=*(phone number)    -   c=*(connection information—not required if included in all        media)    -   b=*(bandwidth information)    -   One or more time descriptions (see below)    -   z=*(time zone adjustments)    -   k=*(encryption key)    -   a=*(zero or more session attribute lines)    -   Zero or more media descriptions (see below)

Time Description

-   -   t=(time the session is active)    -   r=*(zero or more repeat lines)

Media Description

-   -   m=*(media name and transport address)    -   i=*(media title)    -   c=*(connection information—optional if included at session        level)    -   b=*(bandwidth information)    -   k=*(encryption key)    -   a=*(zero or more attribute lines)

The fields marked “*” are optional. For more information on thestructure of SDP data, see the IETF document RFC 2327.

The SDP file relating to a given signaling channel CSi contains a newinformation field m indicating that the channel described by the SDPfile is a signaling channel, “m” signifying “media”, and all theinformation required for a terminal to acquire the signaling channelCSi. For example, the SDP file relating to the signaling channel CS0associated with the main broadcast channel CD0 has the followingstructure:

-   -   v=0    -   s=National station TV1    -   c=IN IP4 224.2.17.12/127    -   m=application 49170 RTP/AVP sig

The field c indicates that the signaling channel is broadcast at themulticast Internet address IP4 224.2.17.12. The field m indicates thatthe channel described is a signaling channel (“sig”), that the signalingchannel uses the RTP, and that the number of the port sending signalingdata carried by the signaling channel is 49170.

The descriptive SDP fields associated with the source S are stored onthe website SW, from which they can be downloaded by the receiverterminals.

The receiver terminals have a web browser enabling them to browse theInternet and an application for receiving broadcast channels that allowseach terminal to acquire a signaling channel associated with a broadcastchannel and to switch from a first broadcast channel to a secondbroadcast channel by acquiring a first signaling channel (CS0)associated with the first broadcast channel (CD0) and then, from thefirst signaling channel (CS0), a second signaling channel (CS1)associated with the second broadcast channel (CD1), and finally toreturn to receiving the second broadcast channel (CD1), from the firstsignaling channel (CS0), as explained later.

The reception method of the invention is described below.

The source S sends IP data packets carrying audiovisual content inmulticast mode on the main channel CD0 and the secondary channels CD1, .. . , CDi, . . . , CDn, together with IP signaling data packets onassociated signaling channels CS0, CS1, . . . , CSi, . . . , CSn.

In a step 1, the receiver terminal T recovers an SDP file associatedwith the source S, in this instance the SDP file relating to thesignaling channel CS0 associated with the main broadcast channel CD0 ofthe source S. To this end, in a step 1a, the terminal T connects to thewebsite SW and, in a step 1b, downloads from that site an HTML pagecontaining links to the broadcast channels CDi of the source S and tocontents broadcast by the source S. In a step 1c, the receiver terminalT selects the link to the broadcast channel CD0 and then sends thewebsite a request to acquire the SDP file relating to the signalingchannel CS0 associated with the broadcast channel CD0. On receiving therequest, in a step 1d, the site SW transmits the required SDP file tothe terminal T via the Internet. In a step 1e, the terminal T stores thedownloaded SDP file and therefore has access to it to enable it toreceive the signaling channel CS0, either immediately after downloadingthe SDP file or later.

In a step 2, to receive the main broadcast channel CD0 of the source S,the terminal T first acquires the signaling channel CS0. To this end, ina step 2a, it sends a request to acquire the signaling channel CS0 viathe Internet, using the Internet Group Management Protocol (IGMP) andinformation contained in the SDP file relating to the signaling channelCS0. The first Internet router that receives the request when it isalready receiving signaling IP data packets broadcast by the signalingchannel CS0 duplicates the IP packets and sends the duplicated packetsto the terminal T in a step 2b. The signaling IP packets are routed viathe Internet to the terminal T, which therefore starts to receive thesignaling channel CS0 associated with the main broadcast channel CD0.

Each signaling channel CSi associated with a broadcast channel CDiconveys the identifier and the type (main or secondary) of the broadcastchannel CDi. For example, the signaling channel CS0 associated with themain broadcast channel CD0 of the national station TV1 carries theidentifier “National station TV1” and indicates that the broadcastchannel CD0 is a main channel. The signaling channel CS1 associated withthe channel CD1 broadcasting programs for a region A carries theidentifier “TV1 regional station A” and indicates that the broadcastchannel CD1 is a secondary channel. Furthermore, each signaling channelCSi carries information needed to receive the associated broadcastchannel CDi, namely the multicast Internet address of the broadcastchannel CDi, the transmission protocol used by the broadcast channel CDi(which is the RTP in this example), and the types of data broadcast(audio, video, etc.), with the numbers of the ports used to send thedata.

In addition to the information relating to the main broadcast channelCD0, the signaling channel CS0 carries information needed to acquire thesignaling channel CSi associated with each secondary broadcast channelCDi, namely, for each signaling channel CSi:

-   -   the identifier of the associated secondary broadcast channel CDi        (TV1 regional station A);    -   the indication of the broadcast computer network (IN=Internet);    -   the computer address of the signaling channel CSi (IP4        224.2.17.13);    -   an indication whether the main channel CD0 and the secondary        channel CDi are broadcast simultaneously (sim=1) or alternately        (sim=0); and    -   where applicable, an indication of the time the channel CDi        starts broadcasting (t_start=2873397496) and an indication of        the time the channel CDi stops broadcasting (t_stop=2873404696).

The information in parentheses is provided by way of illustrativeexample and relates to the signaling channel CS1 associated with thechannel CD1 broadcasting programs to region A.

The signaling channel CSi associated with each secondary broadcastchannel CDi contains, in addition to the information relating to thebroadcast channel CDi, information needed to acquire the signalingchannel CS0 associated with the main broadcast channel CD0, namely theidentifier of the main channel CD0 (National station TV1), theindication of the broadcast computer network (In=Internet), the computeraddress of the associated signaling channel CS0 (IP4 224.2.17.12), andwhere applicable an indication of the time the second channel CDi stopsbroadcasting (for example t_stop=2873404696).

In a step 3, using the signaling channel CS0, the terminal T begins toreceive the main broadcast channel CD0. To this end, in a step 3a, thesignaling channel CS0 supplies the terminal T with the informationrequired to receive the broadcast channel CD0. Using that information,in a step 3b, it sends a request to acquire the main broadcast channelCD0 over the Internet using the IGMP and information contained in thesignaling channel CS0. In a step 3c, the first Internet router thatreceives the request when it is already receiving IP data packetsconveying the content broadcast by the main channel CD0 duplicates theIP data packets and sends the duplicated packets to the terminal T. TheIP packets are routed to the terminal T via the Internet. Thus theterminal T starts to receive the broadcast channel CD0 and receives thecontent broadcast over the channel CD0.

In a step 4, the terminal switches from the main broadcast channel CD0to the secondary broadcast channel CD1. To this end, in a step 4a, thesignaling channel CS0 supplies the terminal T with the informationrequired to acquire the signaling channel CS1 associated with thesecondary broadcast channel CD1. Using that information, in a step 4b,the terminal T sends a request to acquire the signaling channel CS1associated with the secondary broadcast channel CD1 over the Internetusing the IGMP. In a step 4c, the first Internet router that receivesthe request when it is also receiving the signaling IP data packetsbroadcast over the channel CS1 duplicates the signaling IP packets andsends them to the terminal T. The signaling IP packets are routed viathe Internet to the terminal T. Thus the terminal T starts to receivethe signaling channel CS1. In a step 4d, the signaling channel CS1supplies the terminal T with all the information it needs to startreceiving the associated broadcast channel CD1. In a step 4e, using thatinformation, the terminal T sends a request to acquire the associatedsecondary broadcast channel CD1 over the Internet using the IGMP. In astep 4f, the first Internet router that receives the request when it isalready receiving IP data packets conveying the content broadcast by thesecondary channel CD1 duplicates the IP data packets and sends theduplicated packets to the terminal T. The IP packets are routed via theInternet to the terminal T, which starts to receive the secondarybroadcast channel CD1 and receives the content broadcast by the channelCD1.

In a step 5, the terminal T switches from the secondary channel CD1 tothe main channel CD0. To this end, in a step 5a, the signaling channelCS1 associated with the broadcast channel CD1 it is receiving suppliesthe terminal T with the information needed to acquire the channel CS0,namely the identifier of the main channel CD0 and the Internet addressof the signaling channel CS0 associated with the main channel CD0. Usingthat information, in a step 5b, the terminal T acquires the signalingchannel CS0 and then, in a step 5c, from the signaling channel CS0, itacquires the main broadcast channel CD0, as previously described forsteps 3a-c.

When the terminal T is receiving the main broadcast channel CD0, theassociated signaling channel CS0, where applicable, informs it of thestarting and stopping of parallel (i.e. simultaneous) broadcasting viathe secondary channels CDi. Using this information, as soon as asecondary channel is broadcasting a content when the main channel isalready broadcasting a content, the terminal T displays an icon toinform the user of parallel broadcasting via the secondary channel. Theuser can then select the icon and thereby activate a command to switchto the secondary channel. The terminal T then executes above-describedstep 4.

When the terminal is receiving the content broadcast by a broadcastchannel CDi, the associated signaling channel CSi indicates when thecurrent broadcast stops. Using this information, when broadcasting stopson the channel it is receiving, the terminal could automatically switchto another broadcast channel CDi, whether the latter is a defaultchannel or a channel previously programmed by the user. For example,when broadcasting on a secondary channel stops, the terminal couldswitch automatically to the main channel. It is also possible toenvisage enabling the user to program an automatic broadcast channelchange at a given time, at the end of the broadcasting of a specificcontent, or when a particular secondary broadcast channel starts up.

It should be emphasized here that the signaling channel CS0 associatedwith the main broadcast channel conveys the information necessary foracquiring the signaling channels associated with all the secondarybroadcast channels CDi. However, the signaling channel associated witheach secondary broadcast channel CDi carries only the information neededto acquire the signaling channel CS0 associated with the main broadcastchannel CD0, to the exclusion of information needed to acquire thesignaling channels associated with other secondary broadcast channels.Accordingly, the terminal must switch from one secondary broadcastchannel to another secondary broadcast channel via the signaling channelassociated with the main broadcast channel. This limits the quantity ofinformation conveyed via the signaling channels associated with thesecondary broadcast channels and limits the problem of dynamicallyupdating those channels.

In the description above, the broadcast channels of the source S form ahierarchical group in which all secondary channels are linked to themain channel.

As a general rule, the contents are broadcast by a plurality ofbroadcast channels associated with a plurality of respective signalingchannels and forming a group of channels. Each signaling channelassociated with a broadcast channel supplies the terminal T with theinformation needed to acquire one or more other signaling channelsassociated with another broadcast channel of the same group, so that theterminal T can access all the broadcast channels of the group. Forexample, a group of broadcast channels organized into a hierarchydifferent from that described could be envisaged, for instance with asecondary channel being the main channel of a plurality of channels, ora group of non-hierarchical broadcast channels (for example to broadcastpictures from a plurality of cameras filming the same event fromdifferent angles). In which case, the signaling channel associated witheach broadcast channel can convey all the information needed to acquirethe signaling channels associated with all other broadcast channels.

The server S in FIG. 1 could be replaced by a plurality of serversbetween which the load of the various channels is spread.

The invention could be applied to a computer network other than theInternet.

1. A method of reception, by a terminal (T), of content broadcast over acomputer network by a plurality of broadcast channels (CD0, CD1, . . . )forming a group of channels linked in accordance with a givenorganization, in which method: each broadcast channel (CD0, CD1, . . . )is associated with a signaling channel (CS0, CS1, . . . ) conveyinginformation for acquiring said broadcast channel (CD0, CD1, . . . ), theterminal (T) acquires a first signaling channel (CS0) associated with afirst broadcast channel (CD0) and, from said first signaling channel(CS0), starts to receive the first broadcast channel (CD0), and toswitch from the first broadcast channel (CD0) to a second broadcastchannel (CD1) linked to the first broadcast channel (CD0), the terminalT acquires a second signaling channel (CS1) associated with a secondbroadcast channel (CD 1) from the first signaling channel (CS0) and,from the second signaling channel (CS1), starts to receive the secondbroadcast channel (CD1).
 2. A method according to claim 1, wherein, toswitch from the second broadcast channel (CD1) to the first broadcastchannel (CD0), the terminal (T) acquires the signaling channel (CS0)associated with the first broadcast channel (CD0) from the signalingchannel (CS1) associated with the second broadcast channel (CD1).
 3. Amethod according to claim 1, wherein the signal channel (CS0, CS1)associated with one of the broadcast channels (CD0, CD1) indicates tothe terminal (T) whether the two broadcast channels (CD0, CD1) arebroadcasting simultaneously or alternately.
 4. A method according toclaim 1, wherein the signaling channel (CS0, CS1) associated with one ofthe broadcast channels (CD0, CD1) supplies the terminal (T) with acomputer address of the signaling channel (CS1, CS0) associated with theother broadcast channel (CD1, CD0).
 5. A method according to claim 1,wherein the signaling channel (CS0, CS1) associated with one of thebroadcast channels (CD0, CD1) supplies the terminal (T) with anindication of the starting of broadcasting via the other broadcastchannel (CD1, CD0).
 6. A method according to claim 1, wherein thesignaling channel (CS0, CS1) associated with one of the broadcastchannels (CD0, CD1) supplies the terminal with an indication of thestopping of broadcasting via the other broadcast channel (CD1, CD0). 7.A method according to claim 6, wherein the terminal (T) uses theindication of stopping of broadcasting to change broadcast channel (CD1,CD0) automatically when broadcasting stops.
 8. A method according toclaim 1, wherein, during reception of the content broadcast by one ofthe broadcast channels (CD0, CD1), the terminal (T) signals to a userconcomitant broadcasting via the other broadcast channel (CD1, CD0) andchanges broadcast channel in response to a switching command from saiduser.
 9. A method according to claim 1, wherein each signaling channelsupplies the terminal (T) with information for acquiring one or moreother signaling channels associated with another broadcast channel ofsaid group so that the terminal can access all the broadcast channels ofthe group.
 10. A method according to claim 9, wherein the group ofchannels comprises a main channel (CD0) and a plurality of secondarychannels (CD1, . . . , CDi, . . . , CDn) and the signaling channelassociated with the main channel (CD0) supplies the terminal (T) withthe information to acquire signaling channels (CS1, . . . , CSi, . . . ,CSn) associated with all the secondary channels (CD1, . . . , CDi, . . ., CDn).
 11. A method according to claim 10, wherein the signalingchannel (CS1, . . . , CSi, . . . , CSn) associated with each secondarychannel (CD1, . . . , CDi, . . . , CDn) supplies the terminal (T) withinformation for acquiring the signaling channel (CS0) associated withthe main channel (CD0), to the exclusion of information for thesignaling channels (CS1, . . . , CSi, . . . , CSn) associated with theother secondary channels (CD1, . . . , CDi, . . . , CDn).
 12. A methodaccording to claim 10, wherein the signaling channel (CS1, . . . , CSi,. . . , CSn) associated with each secondary channel (CD1, . . . , CDi, .. . , CDn) supplies the terminal (T) with information for acquiring thesignaling channel (CS0) associated with the main channel (CD0) andinformation for acquiring another signaling channel (CS1, . . . , CSi, .. . , CSn) associated with another broadcast channel (CD1, . . . , CDi,. . . , CDn) of the same group.
 13. A terminal for implementing themethod according to claim 1, comprising means for acquiring a signalingchannel associated with a broadcast channel and means for switching froma first broadcast channel to a second broadcast channel adapted toacquire a first signaling channel (CS0) associated with the firstbroadcast channel (CD0) and then, from said first signaling channel(CS0), a second signaling channel (CS1) associated with the secondbroadcast channel (CD1), and finally to start to receive the secondbroadcast channel (CD1) from the first signaling channel (CS0).